An image forming apparatus such as copier, printer, and facsimile may include an optical writing unit (or optical scanning unit) to scan a surface of an image carrier with a light beam, based on original image information, to form a latent image on the image carrier. The latent image can be later developed as toner image.
Such optical writing unit (or optical scanning unit) includes a light source, a polygon mirror, and optical elements such as lens, for example.
A light beam emitted from the light source can be deflected by the polygon mirror, and then focused on the image carrier via the optical elements such as lens. In other words, the light beam scans the surface of the image carrier with such process.
In such optical writing unit, a scanning line formed on the image carrier by the light beam may be curved or inclined with respect to a correct condition by several factors. Such factors may include physical property of optical elements, distortion of housing of the optical writing unit, parts deformation by heat such as heat-accumulated polygon motor, installation distortion of the image carrier, for example.
FIG. 1 schematically shows a curving or inclination of scanning line formed on an image carrier such as photoconductive member. Such curving or inclination of scanning line may occur due to the above-mentioned factors.
An amount of curving or inclination of scanning line may vary depending on conditions of image forming apparatuses, and is in a range of μm order, in general. For example, such curving or inclination may be in a range of 15 μm to 50 μm for one condition, and 150 μm to 200 μm for another condition.
Such curving or inclination of scanning line may cause unfavorable effect as below.
For example, when the scanning line may be curved or inclined with respect to a correct condition, a latent image may not be correctly formed on the image carrier, by which an incorrect image may be formed on a recording medium.
In case of a monochrome image forming or single-color image forming, a little amount of curving and inclination of scanning line may not cause a degradation on image quality, and thereby a user may not recognize an image formed on a recording medium as abnormal image.
However, in case of a color image forming apparatus of a tandem arrangement type using a plurality of image carriers for superimposing a plurality of color images on a recording medium, an inclination deviation of scanning lines between the plurality of image carriers may cause a degradation on image quality even if such inclination deviation of scanning lines is not so significant, and thereby a user may recognize an image formed on a recording medium as abnormal image.
A background art optical scanning unit, which may adjust a curving of scanning line, is shown in FIG. 2. FIG. 2 is a schematic cross-sectional view of a long-shaped plastic lens in a background optical scanning unit.
The optical scanning unit includes a light source such as plurality of LD (laser diode) units (not shown), a long-shaped plastic lens 151, a lens holder 152, and a housing 166, for example. As shown in FIG. 2, the lens holder 152 holds the long-shaped plastic lens 151.
The long-shaped plastic lens 151 can be disposed in a light path of a light beam emitted from the light source. The light beam passed through the long-shaped plastic lens 151 scans a surface of an image carrier such as photoconductive member.
As also shown in FIG. 2, the optical scanning unit also includes adjustment screws 158a and 158b. The adjustment screws 158a and 158b can be used to integrally tilt the long-shaped plastic lens 151 and lens holder 152 in a given direction to correct an inclination of scanning line formed on an image carrier such as photoconductive member.
Specifically, by rotating the adjustment screws 158a or 158b, the long-shaped plastic lens 151 can be tilted in a right or left side in FIG. 2, by which a posture of long-shaped plastic lens 151 may be changed. If the posture of long-shaped plastic lens 151 is changed, an inclination of scanning line on the image carrier may be changed.
Accordingly, the long-shaped plastic lens 151 can function as an adjustment device for adjusting an inclination of scanning line, formed on the image carrier. In other words, an inclination of scanning line on the image carrier can be adjusted by adjusting a posture of long-shaped plastic lens 151.
In such optical scanning unit, the adjustment screws 158a and 158b are rotatable to change the posture of the long-shaped plastic lens 151 as above-mentioned.
In general, an inclination of scanning line can be adjusted by adjusting the posture of the long-shaped plastic lens 151 with the adjustment screws 158a and 158b before shipping an image forming apparatus from a factory.
When such image forming apparatus is used in a user environment over the time, such image forming apparatus may need adjustment of an inclination of scanning line formed on an image carrier. In such a case, a maintenance person may manually rotate the adjustment screws 158a and 158b to adjust an inclination of scanning line although such manual work may not be a user-friendly operation.
FIG. 3 shows another adjusting unit for adjusting an inclination of scanning line.
FIG. 3 shows a lens unit 250 including a long-shaped lens 251, and a bracket 252. The bracket 252 holds the long-shaped lens 251.
As also shown in FIG. 3, the adjusting unit further includes a drive motor 256, and a screw 258. The screw 258 is attached to a shaft of the drive motor 256.
When the screw 258 is moved in an upward direction in FIG. 3, the lens unit 250 can be moved in a direction shown by an arrow D at the drive motor 256 side of the lens unit 250.
Specifically, when the screw 258 is moved in an upward direction in FIG. 3, the lens unit 250 can be moved in an upward direction against a biasing force of a leaf spring 261 at the drive motor 256 side of the lens unit 250. With such upward movement of the lens unit 250, the lens unit 250 may tilt toward a right side using a support member 266 as fulcrum, by which a posture of the lens unit 250 can be changed.
On one hand, when the up-and-down screw 258 is moved in a downward direction in FIG. 3, the lens unit 250 can be moved in a downward direction with biasing force of the leaf spring 261 at the drive motor 256 side of the lens unit 250. With such downward movement of the lens unit 250, the lens unit 250 may tilt toward a left side using the support member 266 as fulcrum, by which a posture of the lens unit 250 can be changed.
An image forming apparatus having such adjusting unit may form a latent image of test image pattern on an image carrier such as photosensitive member at a given timing. The image forming apparatus develops the test image pattern (i.e., latent image) as toner mage by conducting an actual operation process. Then, a pattern sensor (e.g., optical sensor) checks the test image pattern (i.e., toner image).
Based on a result detected by the pattern sensor (e.g., optical sensor), a central processing unit (CPU) controls a rotation angle of the drive motor 256 to change a posture of the lens unit 250.
With such configuration, an inclination of scanning line on the image carrier such as photosensitive member can be adjusted to a given value. Furthermore, such adjustment of the scanning line can be automatically conducted, and thereby a maintenance personnel may not be in need for adjusting an inclination of scanning line.
However, the above-mentioned related art may have drawbacks as below.
Firstly, a range for changing the posture of the lens unit 250 by moving the screw 258 with a rotation of the drive motor 256 may exceed an adjustment effective range of the lens unit 250, wherein the adjustment effective range may be determined by several factors such as optical or physical property of optical parts, for example.
If the posture change range of the lens unit 250 may exceed the adjustment effective range of the lens unit 250, an incidence light may not enter the lens unit 250 with an appropriate angle, by which an adjustment of scanning line may not be conducted properly.
Secondly, an external shock, which may occur to an image forming apparatus having an adjusting unit during a shipment or transportation of image forming apparatus, may cause unfavorable effect.
For example, such external shock may significantly moves the drive motor 256 side of the lens unit 250 although the leaf spring 261 applies biasing force to the drive motor 256 side of the lens unit 250. In such a case, the screw 258 may be disengaged from the lens unit 250 for a short period of time, and then the screw 258 may contact the lens unit 250 again with biasing force of the leaf spring 261.
If the screw 258 and the lens unit 250 can be contacted again with an original condition, which is set in the factory, the image forming apparatus may conduct an image forming operation without trouble.
However, if the screw 258 and the lens unit 250 cannot be contacted again with the original condition, which is set in the factory, or if the leaf spring 261 deforms plastically, the image forming apparatus may have a trouble for conducting an image forming operation.
If the screw 258 and the lens unit 250 cannot be contacted again with the original condition, or if the leaf spring 261 deforms plastically, the lens unit 250 may not be correctly moved in an upward or downward direction by the screw 258 driven by the drive motor 256.
Accordingly, an adjustment of scanning line may not be conducted properly because the screw 258 and the lens unit 250 may not contact each other with the original condition due to an external shock.